Conventionally, in a plant, a factory, etc., to realize a sophisticated automatic operation, distributed control systems (DCS) in which a field device (a measurement device, an operation device) and a control apparatus which performs control thereof are connected via a communications device are being built. While most field devices which configure such distributed control systems performs wired communications, devices for conducting wireless communications which are compliant with industrial wireless communications standards such as ISA100.11a, Wireless HART (registered trademark), etc., (wireless field device) are also being realized in recent years.
In a housing of the above-described wireless field device are generally included an input/output device which performs measurement or operation of the state amount (for example, pressure, temperature, flow amount, etc.) in an industrial process, a wireless communications device which conducts wireless communications in compliance with the above-described industrial wireless communications standards, and a control device which controls and manages an operation of the wireless field device, the respective devices being operated with power supplied from a single power supply. Here, it is not necessary to connect the wireless field device to a communications line or a communications bus like a conventional field device and the wireless field device is basically installed solely in the plant, etc., so that most of the wireless field device has a battery embedded as the above-described single power supply.
Patent document 1 below discloses a wireless device which is installed in a conventional field device not having the wireless communications device to operate the conventional field device as the above-described wireless field device. More specifically, the wireless device disclosed in Patent document 1 below includes an interface connected to the conventional field device, a wireless communications device which conducts wireless communications, and a power supply device which supplies power to the conventional field device via the interface. When a signal from the field device is input via the interface device, this wireless device transmits the signal from the wireless communications device to a transmission destination (for example, an upper-level controller), and, when a signal destined for the field device is received in the wireless communications device, it outputs the signal received via the interface device to the field device.